In conventional art, as a type of combined machining turning machine, a combined machining turning machine has been known which includes a Y axis as an additional axis perpendicular to the X (workpiece radius direction)-Z (workpiece axis direction) plane and which can perform a drilling process on a position separated in the Y axis direction from the X coordinate axis.
As another type, a turning machine has been known having a C axis that holds a workpiece and of which the rotational position is controlled, an X axis of which the position is controlled to approach and separate with respect to the center of the C axis, a Z axis that similarly moves in the axis direction of the C axis, and a turret axis (H axis) that is driven by the X axis and the Z axis and that can rotate at any angle to be perpendicular to the axis line of the C axis. Such a turning machine can perform a planar machining process in the circumferential direction of the workpiece by the use of a virtual Y axis which is not actually present, in addition to a normal turning process on the circumferential surface of a workpiece. This machining process is called a D-cut, in that a cross-section similar to letter D is obtained by linearly cutting off a part of a circular cross-section.
When the D-cut machining process is performed on both sides of a workpiece, a double D-cut (may be referred to as a spanner cut, in that the cross-section of a machined workpiece has a shape similar to the opening of a spanner) having a shape in which both sides of a circular cross-section are cut out is obtained. Such a shape can be obtained by performing the D-cut machining process twice by the use of the machine of the conventional art.
In order to implement the D-cut machining process by the use of the machine having the latter type, a plane separated from the center by an arbitrary distance in the radius direction of a workpiece held on the C axis is imagined, a rotating tool on the H axis is made to face the center of the C axis, the H axis rotates so as to direct the tool in the direction of the center of the C axis at a position separated from the center of the C axis, and the C axis rotates so as to be perpendicular to the tool. At this time, since a position separated in the Y axis direction from a line connecting the center of the C axis and the center of the H axis is a machining point, a machining surface and a tool tip are separated from each other. Accordingly, it is necessary to calculate this distance and to move the center of the H axis toward the center of the C axis (in the X axis direction). By performing this series of controls continuously from one end to the other end of a plane imagined on the circumference of a workpiece on the C axis so that a speed along the virtual Y axis is a command speed, a desired machining process can be embodied. The position of the X axis is controlled depending on the distance of a tool tip (=machining point) from the center of the workpiece.
Patent Reference 1 discloses that a rotational motion of a C axis and a rotational motion of a tool (turret axis) are mechanically synchronized to implement the above-mentioned machining process. Patent Reference 2 discloses a configuration of a machine having six sets, each of which has a configuration implementing the same operation as described above through the use of overall servo control, and an operating method thereof. These patent references describe structure of a machine or operations of respective elements thereof, whereby it is possible to perform a so-called D-cut machining process or a drilling process on a plane of the D-cut surface, under the control thereof.
Machining details similar to the D-cut machining process are shown in Patent Reference 3, but since it is a machine having an X axis, a Z axis, a spindle/C axis, and a fixed-angle dividing turret, Y axis control cannot be controlled. Accordingly, when a drilling process is performed on an outer circumferential surface of a workpiece, all directions of formed holes are directed to the center of the workpiece and thus the holes perpendicular to the plane of the D-cut surface of the spanner-cut surfaces cannot be formed.
[Patent Reference 1] JP-B-H03-033441 (related description: line 32 of column 16 of page 8 to line 28 of column 17 of page 9, line 18 of column 18 of page 9 to line 29 of column 19 of page 10, FIG. 3, and FIG. 4)
[Patent Reference 2] JP-A-2000-218422 (related description: line 25 of column 7 of page 5 to line 34 of the same column, line 25 of column 18 of page 10 to line 32 of column 19 of page 11, FIGS. 7 to 11)
[Patent Reference 3] JP-A-S60-044239 (related description: column 4 of page 5 to line 17 of column 2 of page 6, the linear shape (1e) of the outer circumferential machining in FIG. 10)